SARAH FERGUSON, PRESENTER: It's the drug Grant Hackett described as evil and its abuse was the shame of the Australian men's swimming relay team at the London Olympics. The sleeping pill Stilnox has become associated with elite sport for all the wrong reasons.

Now the National Rugby League is weighing in.

As the NRL starts testing players for using Stilnox, a club doctor has told 7:30 its use as a party drug is widespread in the league and it's becoming popular in other codes as well.

Madeleine Morris has this report.

SSEVEN NEWS PRESENTER: Olympian Grant Hackett has flown to the US to seek treatment for a prescription drug addiction. He's seeking help for dependency to the sleeping drug Stilnox.

REPORTER: Do you think Grant's in a bit of denial?

NEVILLE HACKETT: No doubt, no doubt.

MADELEINE MORRIS: Over the past decade Stilnox has quietly infiltrated the world of sport.

DR PETER LARKINS, SPORTS PHYSICIAN: Certainly in the night-time training, night-time competitions, athletes are often wired up, they're re playing the events in their head, so they don't get the rest. And unless you're going to meditate or you count sheep, you know, sometimes doctors will, in the short term, give them a sleeping tablet to help them get settled again back into their normal sleeping pattern.

DENIS COTTERELL, GRANT HACKETT'S FORMER COACH: I didn't know about it. I really thought it was just using it in, you know, in a needs be basis.

MADELEINE MORRIS: Denis Cotterell was Grant Hackett's coach for much of the swimmer's career. He still trained in the same pool on the Gold Coast where the young Hackett first rose to prominence.

DENIS COTTERELL: Over the years he'd been handling the circumstances, travelling, nerves before races. What we didn't know at the time, we're very naive, with sleeping tablets it provided that escape. It provided the certainty of a good night's sleep. Taking them all those years unaware they actually had an addiction.

MADELEINE MORRIS: Denis Cotterell believes Stilnox left Hackett zoned out in the pool at the Beijing Olympics, costing him gold.

DENIS COTTERELL: He won't say so and he doesn't look for excuses, but I feel for sure, for sure it did.

MADELEINE MORRIS: Last month the extent of Hackett's enduring Stilnox addiction was revealed. He was caught on camera semi naked at Crown Casino searching for his young son who'd gone missing in the middle of the night.

The incident finally tipped him into rehab.

But Grant Hackett was by no means the only swimmer with a Stilnox habit.

SPORTS COMMENTATOR: The US continue to strengthen their lead. This is a bit of a shock.

DENIS COTTERELL: It was freely distributed for the team for a professional reason. You do that continuously for 10 years of your career, it's impossible if the substance you're taking happens to be addictive, well, you're going to become addicted to it.

DR JOHN MAYHEW, CLUB DOCTOR, NZ WARRIORS: The problem is quite prevalent in the NRL with the mixing of Stilnox, benzodiazepine, alcohol and caffeinated drinks. I've had that communication from players themselves and also from players talking about other players that are in their teams and this is just not in the New Zealand scenario, it's in Australia and teams outside of Sydney as well.

MADELEINE MORRIS: John Mayhew is the doctor for the NRL's New Zealand Warriors. In this exclusive interview with 7:30 he's the first club doctor to speak openly about the extent of sleeping drug abuse in the code.

DR JOHN MAYHEW: Widespread is the word I'd use. It's not restricted to one or two clubs. I think it's a problem which is involved in the NRL and also following discussion with people in other codes, it's a problem in other codes of rugby as well.

MADELEINE MORRIS: When Stilnox is taken with energy drinks or alcohol it produces an amphetamine like high. The effect of this cocktailing, as it's known, is what's so appealing for elite athletes.

DR JOHN MAYHEW: Common recreational drugs, cannabis and things like that which show up on drug testing and the athlete would be banned for two years if he used that sort of medication. Whereas Stilnox and the associated drugs are not banned by WADA or any of the other drug agencies. So basically they get a high which is not contrary to any of the drug testing protocols.

MADELEINE MORRIS: The NRL is so worried that as the new season gets under way a new drug testing regime has also been launched. Along with tests for steroids and performance enhancers, players will now be sampled for Stilnox and other prescription drugs.

DR SAM SORRENTI, NRL DOCTORS' ASSOCIATION: If a player tests positive for Stilnox or any of those other medications, for this year on the first occasion they will be counselled, they will be told and again explained to them what they've done wrong, how not to do it and not to do it again. If they're then tested positive a second time then the full brunt of the law will be applied to them.

MADELEINE MORRIS: Under the new policies Zolpidem is not formally banned but its use is strongly discouraged. A full ban is being considered for next year.

PROF. KERRYN PHELPS, GP AND SOCIAL COMMENTATOR: My advice to elite athletes would be to stay completely away from Stilnox. The Australian Olympic Committee has banned the use of Stilnox and I think that's for good reason.

MADELEINE MORRIS: Prominent GP Dr Kerin Phelps is a vocal critic of Stilnox, not only for athletes.

PROF. KERRYN PHELPS: This is the sort of bizarre behaviour that you can see.

(Footage of a girl on Stilnox shown)

MADELEINE MORRIS: Stilnox's possible side effects such as sleepwalking are well documented in the scientific literature as well as in videos posted on the Internet and Dr Phelps says amongst her patients.

PROF. KERRYN PHELPS: There's one example of a patient, for example, who woke up having taken Stilnox and found herself inexplicably on the balcony of her high rise apartment. Now who knows what could have happened if she hadn't woken. There are other patients who describe bizarre behaviours. Eating when they didn't realise they'd been eating in the middle of the night.

I think that there should be consideration for this drug to be banned.

MADELEINE MORRIS: But not every doctor believes banning Stilnox is the answer.

DR PETER LARKINS, SPORTS PHYSICIAN: It's an overreaction because of bad behaviour on a few individuals, but I guess it's a safety net that's been thrown out by the NRL now so they don't continue to get that publicity.

MADELEINE MORRIS: Dr Peter Larkins has worked with AFL clubs and Olympic athletes for decades. He says Stilnox and other sleeping drugs can have a legitimate role in elite sport.

DR PETER LARKINS: I think we've got to be careful when we're not sort of amplifying what's going on with the Stilnox. Clearly it's got side effect problems; I'm not denying that in any way, shape or form. But that manifests itself so quickly in its use, that you stop using it very quickly and find the alternative. It's the people that are habitually using Stilnox the wrong way that is giving it its bad reputation.

MADELEINE MORRIS: Are there AFL players using Stilnox?

DR PETER LARKINS: Absolutely there are AFL players, but again it's been on the radar of most doctors for some time and most doctors wouldn't be using it.

PROF. KERRYN PHELPS: The potential side effects are potentially life threatening, it has been attributed to deaths and I think that we need to be very careful about balancing risks and benefits.

I would certainly caution patients away from Stilnox at every opportunity and say let's look at another way of managing this insomnia problem.

SARAH FERGUSON: Madeline Morris reporting.

Response to 7.30 from Sanofi Spox: In 2013, our Sanofi adverse event reporting centre directly received 24 individual reports of suspected adverse events from consumers taking Sanofi's Zolpidem products. This represents a ratio of less than 0.01% of packs sold.